This application claims the benefit of Korean Patent Application Nos. 2001-59165 filed on Sep. 24, 2001, 2001-59166 filed on Sep. 24, 2001, 2001-59167 filed on Sep. 24, 2001, 2001-62528 filed on Oct. 10, 2001, and 2001-63683 filed on Oct. 16, 2001, which are hereby incorporated by reference for all purposes as if fully set forth herein.
1. Field of the Invention
The present invention relates to a radar detector that detects a speed detection system.
2. Discussion of the Related Art
A speed detecting system such as a speed gun is a device that measures the velocity of a moving object by sending out a continuous radio wave and measuring the frequency of reflected wave. Recently, a radar detector, which can detect the speed detecting system, is developed. The radar detector informs a car driver of the presence of the speed gun by detecting laser beam or ultrahigh-frequency wave from the speed gun and converting it into phonetic signs, letters or acoustic signals. The radar detector, generally, utilizes microwave or laser beam.
A conventional radar detector will be described hereinafter in detail with reference to attaching figures.
FIG. 1 is a schematic diagram of showing a principle of a conventional radar detector. As shown in FIG. 1, laser beam or ultrahigh-frequency wave is shot at a driving car from a speed gun (not shown). The frequency of the ultrahigh-frequency wave from the speed gun may be 10.525 GHz, 24.15 GHz, or 34.7 GHz, which are frequencies in X-band (10.525 GHzxc2x125 MHz), K-band (24.150 GHzxc2x1100 MHz), and Ka-band (34.7 GHzxc2x11.3 GHz), respectively. The speed gun also emits a VG-2 signal, which is a signal for sensing a radar detector of cars. Then, a radar detector detects the laser beam, ultrahigh-frequency wave, or VG-2 signal, and informs a car driver of the presence of the speed gun. The radar detector also transmits jammer or an anti VG-2 signal in order to interfere with signals from the speed gun.
On the other hand, the radar detector provides a car driver with driving information by sensing signals from sensors of railway crossings, foggy regions, or deceleration regions.
FIG. 2 is a block diagram of a conventional radar detector. In FIG. 2, a radar detector includes an antenna 10, a first local oscillator 20, a first filter 30, a first mixer 40, an intermediate frequency amplifier 50, a second local oscillator 60, a second mixer 70, a second filter 80, a demodulator 90, a central processing unit (CPU) 100, a memory part 110, and an indicator 120.
As shown in the figure, high frequency signal from a speed gun (not shown) received by the antenna 10, which is a born antenna, is input into the first mixer 40. At the first mixer 40, the received high frequency signal is mixed with the output signal of the first local oscillator 20, which is a local voltage controlling oscillator. A radar detector using the local voltage controlling oscillator has advantages such as low power consumption and high sensitivity. At this time, in the output signal of the first local oscillator 20, signal of a predetermined band, i.e. noise, is removed via the first filter 30 between the first local oscillator 20 and the first mixer 40. The output signal of the first mixer 40 is amplified by the intermediate frequency amplifier 50, and input to the second mixer 70. At the second mixer 70, the amplified signal is mixed with the output signal from the second local oscillator 60, and modulated to frequency of tie output signal. Next, only the signal of a desired frequency band is taken out via the second filter 80 from the output of the second mixer 70, and then input into the demodulator 90. At the demodulator 90, the input signal is converted from analog values to digital values in order to be input into the CPU 100.
The CPU 100 controls the oscillators 20 and 60 by generating signal, and selects specific signals by comparing the demodulated signals via the demodulator 90 with the data of the memory part 110. The data of the memory part 110 shows relations of frequencies of the ultrahigh-frequency waves received by the antenna 10 and frequencies oscillating via the first and second local oscillators 20 and 60.
The selected result from the CPU 100 is transmitted to a user by sound or a flickering lamp of the indicator 120.
In this radar detector, a beam-lead diode, which can be used in a broadband region, may be used as a first mixer 40 of FIG. 2. FIG. 3 shows the structure of the beam-lead diode of the conventional radar detector. As shown in FIG. 3, the beam-lead diode is made of two diodes, each of which is a Schottky diode. The Schottky diode is a device rectifying alternating currents (AC) by a Schottky barrier, which is a potential barrier between a metal and a semiconductor contacting each other. In such Schottky diode, there is Schottky effect that emission of electrons increases when electric field is applied at the metal, which is emitting thermoelectrons.
FIG. 4 is a circuit diagram of showing a part of a conventional radar detector including a beam-lead diode as a mixer. In FIG. 4, the beam-lead diode 45 mixes the output signal of the antenna 10 of FIG. 2 with the output signal of the first local oscillator 20, which is controlling 5.8 GHz waves, and transmits the mixed signal into the intermediate frequency amplifier 50 of FIG. 2.
FIGS. 5A, 5B, and 5C are graphs of output from a first mixer versus signals of X-band (10.525 GHz), K-band (24.15 GHz), and Ka-band (34.7 GHz) received by the antenna 10 of FIG. 2, respectively, in a conventional radar detector including a beam-lead diode. At this time, output of the first local oscillator 20 of FIG. 2, which is mixed with the received signal by the antenna 10 of FIG. 2, has frequency of 11.49 GHz, 11.665 GHz, and 11.36 GHz.
The radar detector is arranged at a distance of 5 cm from a system of generating initial signal. The system uses Agilent 8722ES Network Analyzer to generate signal of X-band frequency. The signal of X-band, for example 10.525 GHz, is received by the antenna 10, and is mixed with output 11 of 11.49 GHz of the first local oscillator 20 at the beam-lead diode 40 of FIG. 2. The nixed signal is measured by 8566A Spectrum Analyzer of Hewlett Packard and is illustrated in FIG. 5A.
By the above method, signals of K-band and Ka-band are also mixed and illustrated in FIGS. 5B and 5C, respectively.
However, in FIGS. 5A, 5B, and 5C, the output of the beam-lead diode 40 of FIG, 2, i.e. the mixed signal, is unstable and output of power is very small as xe2x88x9238.91 dBm, xe2x88x9239.90 dBm, and xe2x88x9242.98 dBm. The dBm is a unit of power, and 0 dBm is defined as 1 mW at impedance of 50 ohms.
On the other hand, the beam-lead diode as a first mixer should have small capacitance from Schottky contact in order to be used in 30 GHz to 300 GHz band region. Resistance in series from Schottky contact, also, should be small.
The beam-lead diode has to be connected to other elements of the radar detector by packaging, and thus capacitance from the packaging should be small, too. As the packaging of the beam-lead diode has a size of less than 0.5 mm, it is impossible to make the packaging by hand or by surface mount. Therefore, beam-lead of the beamn-lead diode is formed by setting lead on a substrate, and the process needs an expensive apparatus.
Moreover, in the conventional radar detector, the output from the first local oscillator 20 of FIG. 2 has bad characteristics. FIG. 6 is a graph of the output from a first local oscillator in a conventional radar detector. The data of FIG. 6 is simulated by Advanced Design System program of the Hewlett Packard. In FIG. 6, the output of the first local oscillator is unstable in about 12.195 GHz band. That is, since the conventional radar detector does not receive signals in various bands, it is difficult to use the conventional radar detector in broadband region.
Accordingly, the present invention is directed to a radar detector that substantially obviates one or more of problems due to limitations and disadvantages of the related art.
An advantage of the present invention is to provide a radar detector that is manufactured easily and that manufacturing expenses are low.
Another advantage of the present invention is to provide a detector that can be used in a broadband region and has a stable output signal.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, a radar detector includes an antenna for receiving a first signal of ultrahigh-frequency, a first local oscillator oscillating a second signal, a first filter removing noise from the second signal oscillated via the first local oscillator, a first mixer mixing the first signal of ultrahigh-frequency with a third signal filtered via the first filter, an intermediate frequency amplifier amplifying a fourth signal mixed at the first mixer, a second local oscillator oscillating a fifth signal, a second mixer mixing a sixth signal amplified via the intermediate frequency amplifier with the fifth signal oscillated by the second local oscillator, a second filter filtering a seventh signal mixed at the second mixer, a demodulator converting analog values of all eighth signal filtered by the second filter into digital values, a memory part storing data of relations between a ninth signal converted via the demodulator and the second and fifth signals oscillated by the first and second local oscillators, a central processing unit controlling the first and second local oscillators and obtaining a result by comparing the ninth signal converted via the demodulator with the data of the memory part, and an indicator showing a user the result obtained by the central processing unit, wherein the first mixer is made of a transistor including a gate terminal getting the first signal of ultrahigh frequency received via the antenna, a drain terminal receiving the second signal amplified via the second amplifier, and a source terminal being grounded.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention.
In the drawings:
FIG. 1 is a schematic diagram of showing a principle of a conventional radar detector;
FIG. 2 is a block diagram of a conventional radar detector;
FIG. 3 is a circuit diagram showing a beam-lead diode of the conventional radar detector;
FIG. 4 is a circuit diagram of showing a part of a conventional radar detector including a beam-lead diode;
FIGS. 5A, 5B, and 5C are graphs of output from a first mixer versus signal of X-band, K-band, and Ka-band, respectively, in a conventional radar detector including a beam-lead diode;
FIG. 6 is a graph of output from a first local oscillator in a conventional radar detector;
FIG. 7 is a block diagram of a radar detector according to the present invention;
FIG. 8 is a circuit diagram of a transistor used as a first mixer of a radar detector according to the present invention,
FIG. 9 is a circuit diagram of showing a pant of a radar detector according to the present invention;
FIG. 10 is a schematic diagram of a coupler of a radar detector according to the present invention;
FIG. 11 is a graph of output from a coupler of a radar detector according to the present invention;
FIG. 12 is a graph of signal input from a first local oscillator into a first mixer in a radar detector according to the present invention;
FIGS. 13A, 13B, and 13C are graphs of output from a first mixer versus X-band, K-band, and Ka-band, respectively, in a radar detector according to the present invention;
FIG. 14 is a circuit diagram of a first local oscillator of a radar detector according to the present invention; and
FIG. 15 is a schematic view of showing a first local oscillator of a radar detector according to the present invention.